Method of copper precipitation in lead-free solder, granulation and separation of (CuX)6Sn5 compounds and recovery of tin

ABSTRACT

The purpose of the present invention is to separate excess coppers leached out in a lead-free solder bath and recover tin with high efficiency. An element X for forming a (CuX) 6 Sn 5  compound between copper and tin in molten lead-free solders is added to separate out a (CuX) 6 Sn 5  compound. Tin is recovered by binding the (CuX) 6 Sn 5  compound by passing thereof through a multi-perforated plate, further generating swirling currents to precipitate and separate the bound (CuX) 6 Sn 5  compounds and removing thereof.

TECHNICAL FIELD

The present invention relates to separating excess copper leached out ina lead-free solder bath and recovering tin from thence in a solderingprocess of such as a printed board having a copper foil and asurface-mounted component having a copper lead wire.

BACKGROUND OF THE ART

Lead-free solder consists chiefly of tin and contains appropriate amountof copper, silver, nickel, bismuth, indium, phosphorus and germanium.Usually, a wetting phenomenon starts around a temperature range of 250°C. and therefore, a soldering process is performed by immersing membersof a printed board and so on in a solder bath heated to the mentionedtemperature range or contacting members of a printed board and so onwith molten solder spouting formed in a solder bath.

However, copper used for a lead wire of a printed board, a member and soon is heated to the mentioned temperature range in the soldering processand elutes into solder. This phenomenon is so-called “copper leaching”.When copper leaching occurs, surface tension and fluidity of moltensolder are affected as a copper concentration in a solder bath rapidlyleads to raise a melting point of solder. As a result, a defect such asa solder bridge, a perforated solder, unsoldering, a cornuted solder, anicicle-formed solder and so on is caused leading to deterioration ofsolder quality.

Therefore, when a copper concentration in a solder bath rises, a part ora whole of solder in the solder bath are to be replaced. Used solderextracted in this process is discarded as it is or Sn is recovered byexecuting some additional process to reutilize as solder material.

As a recovering method of Sn, conventionally, a method utilizing meltingpoint difference, an electrolytic refining method and so on are used.

DISCLOSURE OF INVENTION Problems to be Solved by the Invention

As a conventional Sn recovering method requires a large-scale facilityleading to need for a large installation and further, an equipment suchas a heater consuming flame and large electricity is necessary tomaintain a temperature of an unrefined object high. This forces adangerous and inefficient operation.

The present invention is to solve the above problem and the purposethereof is to provide a method for separating excess copper leached outin a lead-free solder bath and recovering tin from thence.

Means to Solve the Problem

The inventor of the present invention devoted himself to research andcame to have the following findings.

(1) When an adequate amount of elements of Ni, Co, Fe and so on areadded, copper may separate out as a (CuX)₆Sn₅ compound (X is an elementsuch as Ni, Co and Fe). Sn can be recovered by separating this (CuX)₆Sn₅compound.

(2) However, as a particle of the (CuX)₆Sn₅ compound is small and floatsin solder, recovery is not easy. When the compound is left for a longtime resulting in precipitation, recovery becomes easy but this entailsan increase in an energy cost since a solder melting temperature of230˜250° C. ought to be maintained for a long time. Consequently,granulation and precipitation of (CUX)₆Sn₅ compounds is efficient as amethod for separating and removing thereof.

As a result of accumulated researches based on the above findings, theinventor of the present invention has completed the present inventionenabling to separate excess copper leached out in a lead-free solderbath and recover tin with high efficiency from thence.

A subject-matter of the present invention is a method of copperprecipitation in lead-free solder as described in the following (a), amethod of granulation of (CuX)₆Sn₅ compounds as described in thefollowing (b), a method of separation of (CuX)₆Sn₅ compounds asdescribed in the following (c) and a method of recovering tin asdescribed in the following (d).

(a) A method of copper precipitation in lead-free solder for separatingout copper leached out in lead-free solder as an intermetallic compoundand characterized by adding an element X in molten lead-free solder toform a (CuX)₆Sn₅ compound between copper and tin.

(b) A granulation method of (CUX)₆Sn₅ compounds for forming (CUX)₆Sn₅compounds separated out in tin and characterized by passing the(CUX)₆Sn₅ compound through a multi-perforated plate along with tin.

(c) A method of separation of (CuX)₆Sn₅ compounds for separating(CuX)₆Sn₅ compounds separated out in tin and characterized by providinga swirling current to tin mixed with (CuX)₆Sn₅ compounds to causeprecipitation of (CuX)₆Sn₅ compounds and separation thereof.

(d) A method of recovering tin for recovering tin from lead-free soldercontaining eluted copper therein and characterized by recovering tinwith the following processes of (1) to (4).

(1) A process of separating out a (CuX)₆Sn₅ compound by adding anelement X in molten lead-free solder for forming a (CuX)₆Sn₅ compoundbetween copper and tin.

(2) A process of granulation of (CuX)₆Sn₅ compounds by passing separated(CuX)₆Sn₅ compounds through a multi-perforated plate along with tin.

(3) Processes of precipitation and separation of (CuX)₆Sn₅ compounds byproviding a swirling current to tin mixed with bound (CuX)₆Sn₅compounds.

(4) A process of recovering tin by extracting (CUX)₆Sn₅ compounds.

A desirable element X is more than one selected from Ni, Co and Fe inany of the above processes. Further, plural multi-perforated plates haveto be used and a desirable bore diameter of a multi-perforated plateprovided at an upstream is smaller than that of a multi-perforated plateprovided at a downstream.

EFFECT OF THE INVENTION

According to the present invention, tin can be recovered with highefficiency by separating excess copper leached out in a lead-free solderbath. Tin recovered by this means is reutilized as a solder material.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is view illustrating a brief overview of a tin recovering methodwith respect to the present invention.

FIG. 2 is a flame format illustrating a separating method of (CuX)₆Sn₅compounds.

FIG. 3 is a flame format illustrating one example of a granulationmethod of (CUX)₆Sn₅ compounds of the present invention. (a) is anoverall flaming view, (b) is a cross-section view of a granulator and(c) is a development view of a multi-multi-perforated plate providedwithin a granulator.

FIG. 4 is a flame format illustrating a separating method of (CuX)₆Sn₅compounds of the present invention.) (a) shows a state of charging, (b)is a state of agitating swirling currents and (c) is a state ofcessation of agitating swirling currents.

DESCRIPTION OF CODES

-   1 is a precipitation container-   2 is lead-free solders-   3 is a (CuX)₆Sn₅ compound-   4 is a granulation container-   5 is a granulator-   6 is a formed (CuX)₆Sn₅ compound-   7-1 is the first multi-perforated plate-   7-2 is the second multi-perforated plate-   7-3 is the third multi-perforated plate-   8 is a multi-perforated plate-   9 is a metal plate-   10 is a hole-   11 is a separation container-   12 is tin

BEST MODE FOR OPERATING THE INVENTION

Hereafter, an embodiment of the present invention is described withreference to the drawings.

1. A Tin Recovering Method

FIG. 1 is a view illustrating a brief overview of a tin recoveringmethod with respect to the present invention. As shown in this view asto a recovering method of tin of the present invention, firstly, copperleached out in lead-free solder excessively according to “copperleaching” of a printed board and so on is separated out as a designatedcompound and in certain instances, the compound is granulated andafterwards, tin is separated out from this compound. Tin is to bereutilized as renewed solder material and copper compounds are to bediscarded or reutilized as material of copper, tin and so on byrefining.

2. A Method of Separating Out (CUX)₆Sn₅ Compounds

FIG. 2 is a flame format illustrating one example of a separating methodof (CuX)₆Sn₅ compounds. As shown in FIG. 2 with respect to a separatingmethod of the present invention, for example, lead-free solder 2 withcopper leached out excessively is flowed in a precipitation container 1and an appropriate amount of element Xs are added while heating thecontainer to a prescribed temperature range by a heater (not shown inthe Fig.). A (CuX)₆Sn₅ compound 3 is separated out by addition of anelement X. A heating temperature is set above to a dissolutiontemperature of solder and below to an incorruptible temperature ofseparated (CuX)₆Sn₅ compounds, namely, from 230˜250° C. Further, motheralloy, wherein an appropriate amount of element Xs are solved in Sn, canbe added as a method of addition of an element X.

An element X can be any element which is solved in Cu but forms aprecipitate with Sn. For example, Ni, Co, Fe can be cited. When anappropriate amount of these elements are added, a (CuX)₆Sn₅ compoundhaving a crystal structure with a higher melting temperature than solderin molten solder is formed. High purified tin can be recovered byprecipitating and removing the (CuX)₆Sn₅ compound.

However, since a particle of the (CuX)₆Sn₅ compound is small andtherefore buoyant, precipitation thereof takes long time. Meanwhile, aninside of a precipitation container has to be maintained a temperaturerange of 230˜250° C. an increase in energy cost is caused. Consequently,the inventor of the present invention came up with a way of removing(CuX)₆Sn₅ compounds floated in solder after changing thereof to a formeasily recovered. This method is described as below.

3. A Granulation Method of (CUX)₆Sn₅ Compounds

FIG. 3 is a flame format illustrating one example of a granulationmethod of (CuX)₆Sn₅ compounds of the present invention. (a) is anoverall flaming view, (b) is a cross-section view of a granulator and(c) is a development view of a multi-perforated plate provided within agranulator. As shown in FIG. 3, (a) with respect to a granulation methodof the prevent invention, for example, a granulation container 4, aninside of which a granulator 5 is provided, is used.

A (CuX)₆Sn₅ compound 3 is passed through with molten tin 12 in thegranulation container 4. The (CuX)₆Sn₅ compound 3 drifts downward fromnear an upper center in the figure, flows from an inside to an outsideof holes of multi-perforated plates 7-1, 7-2 and 7-3 composing thegranulator 5 and further follows down to an exit. The (CUX)₆Sn₅ compound3 is to bind together every time the (CUX)₆Sn₅ compound 3 passes throughholes of the multi-perforated plates 7-1, 7-2 and 7-3. As a result, aparticle diameter thereof grows larger by degrees.

A granulator 5 is not limited to one shown in the FIG. 3 and forexample, a constitution, wherein a single multi-perforated plate isprovided and passed, can be adopted. However, considering formingefficiency, plural multi-perforated plates may be prepared andmulti-perforated plates 7-1, 7-2 and 7-3 are arranged in a concentricpattern as shown in FIG. 3 (b). Further, a desirable bore diameter of ahole of 7-1 of the first multi-perforated plate provided innermost(namely, at an upstream) is smaller than that of a hole of 7-2 of thesecond multi-perforated plate and a desirable bore diameter of the holeof 7-2 of the second multi-perforated plate is smaller than that of ahole of 7-3 of the third multi-perforated plate as shown in the FIG. 3(b). As to a bore diameter, for example, the first perorated plate 7-1is set to 2 mm, the second multi-perforated plate 7-2 is set to 3 mm andthe third multi-perforated plate 7-3 is set to 4 mm.

A desirable temperature inside a granulation container is kept within230˜250° C. by a heater not shown in a figure as well as a temperatureinside a container in a precipitation method. A wire netting can be usedas a multi-perforated plate but a punching metal, wherein plural holes10 are punched in a metal plate 9 as shown in FIG. 3 (c), is desirableto use from perspectives of intensity and a bore diameter measuresystem.

4. A Separating Method of (CUX)₆Sn₅ Compounds

FIG. 4 is a flame format illustrating one example of a separating methodof (CuX)₆Sn₅ compounds of the present invention. (a) shows a state ofcharging, (b) is a state of agitating swirling currents and (c) is astate of cessation of agitating swirling currents. As shown in the FIG.4 with respect to a separating method of the present invention, forexample, molten tin 12 mixed with bound (CuX)₆Sn₅ compounds is flowed ina separation container 11 as shown in FIG. 4 (a), and afterward swirlingcurrents are to be generated as shown in FIG. 4 (b).

Then, (CuX)₆Sn₅ compounds concentrates gradually at a bottom of a centerof the separation container 11. When swirling currents have ceased,(CuX)₆Sn₅ compounds precipitate at a bottom of a center of theseparation container 11 as shown in FIG. 4 (c). In this state, highpurified tin is left within the separation container 11 and can berecovered by removing bound (CUX)₆Sn₅ compounds from a discharge spoutof the separation container 11 not shown in a figure.

A desirable temperature inside the separation container is kept within230˜250° C. by a heater not shown in a figure as well as a temperatureinside a container in a precipitation method. In the FIG. 4, processesof charge of the molten tin 12 and agitation of swirling currents areillustrated separately to simplify an explanation but these processescan be conducted simultaneously. More specifically, swirling currentscan be occurred within the separation container 11 by adjusting an flowangle of the molten tin 12 mixed with bound (CuX)₆Sn₅ compounds. As to ameans of generating swirling currents, for example, a method wherebyswirling currents are generated within the molten tin 12 mixed with(CuX)₆Sn₅ compounds by inserting an agitating equipment from an upperpart of the separation container 11 or by adjusting an ejectingdirection of a nozzle provided on a side of the separation container 11can be adopted.

As to a recovering method of the molten tin 12 after removing bound(CuX)₆Sn₅ compounds, a method whereby the molten tin 12 can be withdrawnfrom an upper part of the separation container 11 utilizing a pump canbe possible but the pump may be damaged by a temperature of moltensolder. Accordingly, after removing bound (CuX)₆Sn₅ compounds from adischarge spout, the discharge spout is closed for the meanwhile, andthen the molten tin 12 can be discharged in a separate container frombound (CUX)₆Sn₅ compounds. Further, a method whereby the molten tin 12can be recovered by providing a discharge spout for recovering tin neara upper part of a separation container and discharging only supernatantfluid of molten tin can be adopted.

In the above explanation, a method of separating bound (CuX)₆Sn₅compounds is described. Even when a binding process is skipped,(CuX)₆Sn₅ compounds can be separated with the same method requiring moretime.

Each process is explained hereinbefore, and obviously these processescan be conducted in a continuous fashion. In this instance, tin can berecovered in a recycling factory utilizing a method of this invention byrecovering used solder from a dip solder bath or a spout solder bath.Further, this method can be conducted without transferring other placeby installing an equipment enabling to conduct a recovering methodconcerning the present invention beside a dip solder bath or a spoutsolder bath while operating soldering. The latter case is useful foradjusting a copper concentration within a solder bath since copperleached out excessively can be separated continuously.

INDUSTRIAL APPLICABILITY

According to the present invention, tin can be recovered with highefficiency by separating excess copper leached out in a lead-free solderbath. This recovered tin can be reutilized as a solder material.

1. A method of recovering tin from lead-free solder by separating outcopper leached out in lead-free solder as an intermetallic compoundcharacterized by adding an element X to a solder bath to form a(CuX)₆Sn₅ compound between copper and tin in molten lead-free solder andremoving (CuX)₆Sn₅ compounds to recover tin.
 2. A method of recoveringtin from lead-free solder according to claim 1, wherein element X is atleast one element selected from the group consisting of Ni, Co and Fe.3. A tin recovering method for recovering tin from lead-free solder withliquated copper therein and characterized by recovering tin with thefollowing processes of(1) to (4): (1) separating out a (CuX)₆Sn₅compound by adding an element X forming a (CuX)₆ Sn₅ compound betweencopper and tin in molten lead-free solder; (2) binding (CuX)₆Sn₅compounds by passing a separated (CuX)₆Sn₅ compound through amulti-perforated plate with tin; (3) precipitating and separating(CuX)₆Sn₅ compounds by generating swirling currents in tin mixed withbound (CuX)₆Sn₅ compounds; and (4) recovering tin by removing (CuX)₆Sn₅compounds.
 4. A tin recovering method according to claim 3, wherein anelement X is at least one element selected from the group of Ni, Co andFe.
 5. A tin recovering method according to claim 3, wherein pluralmulti-perforated plates are used and a diameter of a multi-perforatedplate provided at an upstream is smaller than that of a multi-perforatedplate provided at a downstream.
 6. A tin recovering method according toclaim 4, wherein plural multi-perforated plates are used and a diameterof a multi-perforated plate provided at an upstream is smaller than thatof a multi-perforated plate provided at a downstream.